The production processes of a semiconductor device are conducted in a clean room, and the semiconductor wafers are frequently washed with pure water, because contaminants such as dusts, mists, and fine particles composed of conductive compound atoms readily jeopardize the property such as the insulation characteristics of the semiconductor devices produced employing the foregoing semiconductor wafers. Unfortunately, however, it is not easy to keep the internal atmosphere of a clean room absolutely clean, and the pure water employed for washing the semiconductor wafers is gradually contaminated. Exemplary contaminants jeopardizing the insulation of a gate insulator layer of a field effect transistor having a gate insulated from a channel layer and/or the insulation of a capacitor are phthalic acid ester which is employed for a draught test of a clean room, dibutyl phthalate which is employed as a plasticizer employable for producing various plastic vessels, boxes, other apparatus or the like, and butyl hydroxy toluene which is employed as a plasticizer employable for producing wafer cases or the like.
For the purpose to identify the contaminants of a contaminated semiconductor wafer before and after a step for producing a gate insulator layer of a field effect transistor, a wafer-heating gas-removing gas chromatography mass spectrometer was employed. FIG. 1 is a gas chromatogram of a gas evaporated from an Si substrate just after being washed with pure water and FIG. 2 is a gas chromatogram of a gas evaporated from an Si substrate on which a gate insulator layer has been produced. It is well known that the Y axis of a chromatogram represents relative strength or detected quantity of a detected compound and the X axis of a chromatogram represents the time at which the foregoing compound was detected or the mass of the compound detected.
For the purpose to identify the contaminants remained unevaporated on an Si water after heating it in N.sub.2 gas for 10 minutes, a wafer-heating gas-removing gas chromatography mass spectrometer was employed. FIG. 3 is a gas chromatogram of a gas evaporated from an Si substrate heated at a temperature range of 500.degree. C. through 700.degree. C. in N.sub.2 gas for 10 minutes. Benchtop/PBM search results show the substances represented respectively by A and B shown in FIG. 3 are 1-(phenyl thio)-1-(trimethylsilyl)-2-propene and (trimethylsilyl) adamantone respectively having a molecular construction respectively shown in FIG. 4A and in FIG. 4B.
Results of an analysis applied to FIGS. 1, 2 and 3 are itemized below.
1. Major contaminants of an Si wafer under progress of a production process for producing a semiconductor device are compounds each of which has a benzene ring therein. PA0 2. A high temperature process conducted for producing a gate insulator layer is effective to remove some volatile sorts of contaminants from the surface of an Si wafer. PA0 3. A heating process applied to an Si wafer on which a gate insulator layer has been produced, the heating process being conducted at a temperature range of 500.degree. C. through 700.degree. C. in N.sub.2 gas for 10 minutes, causes silylyzation to occur for reacting with some of the functional groups alone of the compounds each of which has a benzene ring therein, resultantly converting the compounds to other non-volatile sorts of compounds, such as 1-(phenyl thio)-1-(trimethylsilyl)-2-propene, and trimethylsilyl adamantone. PA0 1. Major contaminants remaining on an Si wafer after a high temperature process for producing a gate insulator layer are non-volatile compounds respectively having a benzene ring therein, such as 1-(phenyl thio)-1-(trimethylsilyl)-2-propene, trimethylsilyl adamantone and the like. PA0 2. An action to cause an Si wafer having the foregoing contaminants thereon to contact with a gas such as the air, oxygen and ozone under a temperature range of 500.degree. C. through 700.degree. C. or with a liquid such as a mixture of sulfuric acid and hydrogen peroxide and a mixture of pure water and ozone causes silylyzation to occur to cleave some of the benzene rings of the foregoing non-volatile compounds, resultantly converting the non-volatile compounds to chain silyl esters or the like which are volatile.
The above results imply a reaction which cleaves benzene rings of the contaminant compounds respectively having benzene rings therein would convert the contaminant compounds to volatile compounds which can readily be removed from the surface of an Si wafer.
As a matter of fact, since most compounds respectively having a benzene ring therein are conductive, such compound contaminants readily jeopardize the insulation of an insulator layer located between a conductor layer of a semiconductor device e.g. a gate insulator layer of a field effect transistor and an insulator layer composing a capacitor produced in a semiconductor device.